1. Field of the Invention
The present invention relates to an attachment structure for a filter which filters working oil in a gear pump.
2. Description of the Relevant Art
Outboard engines for use as power units on small marine vessels such as motorboats are associated with tilt/trim units. The tilt/trim unit comprises a tilt cylinder for angularly moving the outboard engine through a relatively large angle to bring the lower part of the outboard engine into and out of water, and a trim cylinder for angularly moving the outboard engine vertically through a relatively small angle with the lower part of the outboard engine being immersed underwater. The tilt and trim cylinders are supplied with working oil under pressure by a gear pump. The gear pump has a filter disposed near the inlet port, for filtering the working oil.
Heretofore, the filter is held by a filter holder with dampers bonded to upper and lower surfaces of the filter holder. The filter unit, which is composed of the filter and the filter holder, is sandwiched, through the dampers, between the gear pump and the bracket of a motor which actuates the gear pump.
If a gear pump of a different displacement is employed, then the distance between the gear pump and the motor bracket is varied. Therefore, a filter unit which is to be held between the gear pump and the motor bracket must be of such dimensions as to suitably match the varied distance. Stated otherwise, there have to be available as many filter unit types as there are different gear pump displacements. As a consequence, it has been costly to manufacture the filter units. Bonding the dampers to the filter holder is tedious and time-consuming because care should be exercised to appropriately control the amount of an adhesive used. It is also not efficient and easy to attach or replace a filter as the filter holder thereof needs to be sandwiched between the gear pump and the motor bracket.